Modelling the fate of nitrogen in crop and soil in the years following application of ¹⁵N-labelled fertilizer to winter wheat

Abstract

SUMMARYA computer model is presented that describes the flow of nitrogen between crop and soil on the field scale. The model has a compartmental structure and runs on a weekly time-step. Nitrogen enters via atmospheric deposition and by application of fertilizer or organic manures, and is lost through denitrification, leaching, volatilization and removal in the crop at harvest. Organic nitrogen is contained within three of the model compartments – crop residues (including plant material dying off through the growing season), soil microbial biomass and humus. Inorganic nitrogen is held in two pools as NH4+ or NO3-. Nitrogen flows in and out of these inorganic pools as a result of mineralization, immobilization, nitrification, leaching, denitrification and plant uptake. The model requires a description of the soil and the meteorological records for the site – mean weekly air temperature, weekly rainfall and weekly evapotranspiration. The model is designed to be used in a ‘carry forward’ mode – one year's run providing the input for the next, and so on. The model also allows the addition of 15N as labelled fertilizer, and follows its progress through crop and soil. Data from a Rothamsted field experiment in which the fate of a single pulse of labelled N was followed over several years were used to set the model parameters. The model, thus tuned, was then tested against other data from this and two contrasting sites in south-east England. Over a period of 4 years, the root mean square (R.M.S.) difference between modelled and measured quantities of labelled N remaining in the soil of all three sites was c. 7·5 kg N/ha, on average. The root mean square error in the measurements was c. 2·5 kg/ha. Similarly, the R.M.S. difference between modelled and measured recovery of labelled N by the crop was 0·6, compared with 0·3 kg/ha in the measurements themselves.

Effects of amendment of different biochars on soil carbon mineralisation and sequestration

“…The humification coefficient (h) is defined as the fraction of organic matter remaining in the soil after 1 year and is calculated with Eqn 3 by setting t = 365 days (Bradbury et al 1993). The humification coefficient gives an estimation of the stable organic matter remaining in the soil and it is used as an indicator of C sequestration potential (Cayuela et al 2010).…”

How Important is the Quality of Organic Amendments in Relation to Mineral N Availability in Soils?

“…Generally, small pools with high turnover rates (referred to as ''decomposable'' or ''labile'' or ''active'') and larger pools with slower turnover rates (referred to as ''recalcitrant'' or ''resistant'' or ''slow'') are distinguished [14,51,92]. Some models consider microbial biomass as one of the defined pools while others do not include a biomass pool and model it as part of the stable organic matter/humus pool [41, 51,92,119].…”

“…Some models contain few organic matter pools [14,57], some contain multiple pools of microbial biomass and protected and non-protected organic matter [114]; but most have fixed numbers of pools and so their structure is not easy to alter.…”

Validation of Simulated Runoff From Six Terrestrial Ecosystem Models: Results From Vemap

“…3) GTEC hydrology is derived from the SUNDIAL model (Bradbury et al 1993). There are 12 soil layers: 0-50 cm in 5 cm increments, 50-100 cm, and 100-200 cm.…”